This invention relates to fire truck controls, and more particularly to safety apparatus for preventing the speed of the fire truck engine from being increased with its pump throttle control when the engine is operatively connected with the wheels of the fire truck.
In many fire trucks the same engine is used to either propel the fire truck or to drive a pump carried by the fire truck which dispenses water under high pressure to aid in the fighting of fires. Generally, such fire trucks have a transfer box which is coupled through a transmission to the engine. The transfer box is manually shiftable from a first mode in which it operatively connects the engine with the wheels, to a second mode in which it operatively connects the engine with the pump.
Such fire trucks typically have two throttle controls. When the fire truck is being driven, a first throttle control can be manually operated from the cab of the fire truck with an accelerator pedal. There is a large control panel on the side of the fire truck. The second throttle control includes a cable which is connected at one end to the engine and at its other end to an advancement mechanism on the control panel. When the fire truck is parked and the engine is driving the pump, the advancement mechanism can be manually operated to vary the engine speed to ensure proper water flow from the pump.
Early models of fire trucks had manual shift transmissions. When the fire truck arrived at the scene of a fire the driver brought the engine to idle speed and with the clutch pedal depressed the driver shifted the transfer box from its first mode to its second mode. The clutch was then released and firemen could vary the engine speed with the advancement mechanism at the side of the truck to ensure proper water flow from the pump. With such early models it was impossible for the driver to leave the cab with the engine running, the transmission in gear, and the transfer box in its first mode. the truck would lurch forward and stall the instant that the driver released the clutch. Therefore, varying the engine speed with the second throttle control never posed a problem in these early model fire trucks.
Later models of fire trucks use automatic transmissions and this presents a significant safety hazard. In such a later model fire truck it is possible for the driver to pull to a stop and leave the cab with the engine running and the automatic transmission in gear forgetting to shift the transfer box into its second mode (pump drive mode). The only thing that prevents the fire truck from moving at this point is the parking brake (if the driver remembered to set it) and the low engine idle speed. If a fireman increases the engine speed with the second throttle control (at the side of the truck) under these circumstances, with the intent of increasing the pump speed, and the increased engine power overcomes the parking brake, the fire truck will drive away with no one in the cab to control it.
Because of this danger, many later model trucks of this design have a red indicator light on the pump control panel to warn the fireman if the transfer box is still in its first mode. This light is activated by an electrical switch associated with the transfer box. While such a warning light helps to remind the fireman to shift the transfer box before advancing the second throttle control, it can be easily overlooked in the excitement and confusion which occurs at the scene of a fire. Thus, the use of such later model fire trucks involves the risk of a runaway fire truck. Therefore, a more reliable safety apparatus is required.